1. Field of the Invention
The present invention relates to a winding brake for a spring-return tape measure having weights working within a circular path during rotation in the case of drum carrying a graduated tape.
2. The Prior Art
Spring-return tape measures, more generally called tape measures, are generally made up of a drum which, carries the measuring tape and is mounted to rotate freely on a pin integral with a case. The drum is connected to this pin by a coil spring housed inside the case.
Unwinding of the graduated metal tape from the case winds the coil spring which, by elasticity, assures re-winding of the tape as soon as it is released.
This device is entirely satisfactory for tapes with a length of three meters or less but creates a problem for lengths beyond that. Actually, although the coil spring has a length less than that of the graduated tape, in the ratio of diameters, respectively of the drum and pin, its length increases with that of the graduated tape and leads, for graduated tapes of five meters, to a very high return force. Thus, during winding of a tape of great length, the winding coil of the tape assumes, under the recall effect of the coil spring, a rotation speed regularly increasing to become maximum and to reach, for example, a thousand revolutions per minute when the hook strikes the case. Because of this and the progressive increase of the winding diameter of the tape on the coil, the linear speed of the tape also increases. Even if the tape is perfectly aligned with the case before winding, in the last two meters of its winding, it tends to whip, which causes winding defects, damage and even breaking. Moreover, at the end of winding, the impact due to the stopping by the stop of the end hook against the case is very great since the case absorbs a kinetic energy taking into account the total weight of the coil, the diameter of the winding and the great rotation speed of the latter. This impact causes a deterioration of the case, the coil, the fasteners of the coil spring, the tape and the hook.
To eliminate this, it is already known to provide the spring-return tape measure with a brake limiting the rotation speed of the drum, which is made up of weights acting centrifugally. Such a device intervenes both during winding and unwinding, which is bothersome since unwinding should be able to be performed freely. Another drawback of this device is that it increases the weight of the spring-return tape measure, even though, for this type of product, which is carried in the pocket, lightness is important.